1. Field
The present disclosure relates to an apparatus and method for recovery of sulfur hexafluoride.
2. Description of the Related Art
Sulfur hexafluoride (SF6) is a typical electrical dielectric substance used for electric power devices. SF6 is also used for washing process in the manufacture of semiconductor wafers, LCD panels, etc. SF6, however, is known to have an impact on global warming about 23,900 times that of carbon dioxide. Further, in the Convention on Climate Change held in Kyoto in 1997, SF6 was listed as one of six substances with the largest global warming potentials.
There are several methods for treating SF6. The first method is to decompose SF6. Since SF6 is very stable, high energy such as plasma is required to decompose SF6. Further, during the decomposition, highly toxic and corrosive byproducts such as S2F10, SF4 and HF are produced. Considering the problems associated with the decomposition as well as the consistently increasing price of SF6, it would be desirable to recover and recycle SF6 in terms of cost saving.
In order to recover SF6 from SF6-containing mixture gas, general gas separation techniques such as chilling, pressure swing adsorption (PSA), membrane separation, etc. may be employed.
The chilling method is suitable for large-scale, high-concentration applications, but the investment cost is high while the energy consumption efficiency is low. In PSA method, an adsorbent such as zeolite is used to separate SF6 by adsorbing small-sized molecules like nitrogen, and pressurization and decompression are repeated so that the adsorbed substance, e.g. nitrogen, is desorbed during decompression and then fresh nitrogen is adsorbed during the next pressurization, thereby separating SF6 from a nitrogen/SF6 mixture gas. In PSA method, however, SF6 leaks out during desorption. Although the maximum recovery efficiency may be 90% or above, if the ratio of SF6 in the mixture gas is low, liquefaction is necessary after separation, since only about 60 vol % of SF6 is recovered from the mixture gas.